Modern electronic systems, for example, mobile phones, digital cameras and personal digital assistants, have an ever increasing demand for highly-integrated and energy-efficient semiconductor circuits. In order to meet these requirements, the physical size of field effect transistors (FETs) within the semiconductor circuits is reduced. Due to the shrinking size, the FETs become more susceptible to variations of parameters of the semiconductor circuits, like process, supply voltage, aging of the devices, and temperature. Traditionally, these variations are modeled by guard-banding, i.e., safety margins may be added to allow for a robust operation of the semiconductor circuits. However, safety margins are expensive in terms of area and power dissipation.
On-chip monitor circuits may be implemented to measure the actual status of the semiconductor circuits with respect to certain variations. Countermeasures or adaptive techniques may be initiated on a circuit level or a system level responsive to the measurement results of the on-chip monitor circuits. A specific on-chip monitor circuit is typically designed to measure one specific effect, such as the process performance class with high measurement accuracy. Further variations such as process or supply voltage are acting as disturbing effects during the measurement and will reduce the measurement accuracy of a specific on-chip monitor circuit.
A sensitivity of the on-chip monitor circuit to disturbing effects should be as small as possible to avoid a corruption of the measurement results. A thorough design of the on-chip monitor may decrease the sensitivity to disturbing effects. If the sensitivity of the on-chip monitor circuit to disturbing effects cannot completely eliminated, a calibration of the on-chip monitor circuit may be required to compensate for the disturbing effects. The calibration may be performed during fabrication, after fabrication or during operation of the on-chip monitor circuit. The calibration of an on-chip monitor may be implemented by providing a circuitry that modifies the electrical behavior of the monitor, i.e. the monitor operation can be switched between several, predefined configuration settings. During calibration, one specific predefined configuration setting may be selected that provides the best measurement accuracy and stored for later use of the monitor in a measurement mode. The selected configuration setting may be stored in a register, a volatile memory, a nonvolatile memory, or an electrical fuse. The register, the volatile memory, the nonvolatile memory, or the electrical fuse may be implemented on the same semiconductor substrate as the on-chip monitor or implemented on a separate semiconductor substrate.